Comtech EF Data CDM-625A - Manual (Page 697)

CDM-625A Advanced Satellite Modem MN-CDM625A
Appendix M Revision 3
M–17
Step Task Front Panel VFD Mnemonic
5 (SELECT) CONFIG: RX  FEC
Set the Rx FEC type as VersaFEC-2 Long, or
VersaFEC-2 Short Block. Note that this does not
have to match the Tx FEC type.
RxIF Freq FEC Demod Symb Descram Eq EbNo
(Data 02048.000kbps,02184.533ksps)
()
Dec=VF2L(VF2L, VF2S)
Reed-Solomon=Off (Fixed in ACM)
()
6
(SELECT) CONFIG: RX  SYMB
Enter the desired receive symbol rate. Note that
asymmetric operation is supported – transmit and
receive symbol rates do not have to be equal.
RxIF Freq FEC Demod Symb Descram Eq EbNo
(Data 02048.000kbps,02184.533ksps)
()
RxSymbolRate = 01000.000 ksps (ACM Mode)
Data Invert=Off Clock Invert=Off
()
7 (SELECT) CONFIG: ACM 
Configure the desired ACM operating parameters, by
selecting the
ACM submenu from the CONFIG:
menu branch.
Proceeding from the
CONFIG: ACM submenu:
CONFIG: All Mode Tx Rx Clocks ACM
CnC EDMAC Misc Mask Remote IP
()
ACM Config: Min/Max-ModCod Unlock-Action
Target-EbNo-Margin
()
a)  Min/Max-ModCod: Define the range of
ModCods over which the system will operate.
ModCod 0 is fixed at BPSK Rate 0.489 (0.489
bps/Hz), while ModCod 37 is 32-ARY Rate 0.879
(4.397 bps/Hz).
Min Modcod: 00(B 0.489, 0.489 bps/Hz)
Max Modcod: 37(32-ARY 0.879, 4.397 bps/Hz)
In VersaFEC-2, the Minimum ModCod is fixed at 0, and the user cannot change it.
CAUTION – The value of Max ModCod may be limited by other FAST codes installed.
For example, suppose the 4100 ksps FAST option is installed, and the symbol rate set to
4100 ksps, the theoretical maximum data rate would be ~18 Mbps at ModCod 37.
However, is CnC is being used, with a 10 Mbps FAST limit, the ACM Max ModCod will
be limited to ModCod 21, or 9.8 Mbps.
b)  Unlock-Action: For VersaFEC-2 the unlock
action is fixed. In the event that the distant-end
demod loses lock, the Tx ModCod will automatically
go to ModCod 0. When distant-end demod loses lock:
Go to Tx ModCod 0 (Fixed in VersaFEC-2)
c)  Target Eb/No margin: This is a VERY important
parameter. The ACM system is designed to switch
based on thresholds that correspond to a BER of 1 x
10
-8 for each ModCod. However, in order to prevent
oscillation around two ModCods at this exact value,
0.3 dB of hysteresis has been added.
Target Eb/No Margin = 0.5 dB (0.0 – 4.5)
()
8 (SELECT) CONFIG: IP  Switch-set-up  WAN
Enter the desired size of the WAN Buffer. The
minimum size is 20 milliseconds, and is referred to the
data rate corresponding to ModCod 0. Note that this
does not apply if the Packet Processor Card is
installed.
Ethernet Switch: Mode WAN PerPortCnfg
MAC-Learning VLAN Qos Stats (
)